﻿Absorption of X- Rays and Fluorescent X-Ray Spectra. 989 



not only a similarity in general features, but that one ab- 

 sorption curve is common to all absorbing substances. The 

 exactness of this in the case of absorption by Fe, Ni, Gu, Zn, 

 and Br is remarkable, and is illustrated in fig. 1 by a few 

 points obtained from experiments on absorption by each of 

 these elements. Thus in fig. 1, curve K is seen to pass 

 through points indicating absorption by Fe, Ni, Gu, Zn, and 

 Br. In explanation of the notation it should be pointed out 

 that the letters GuFe, for instance, denote absorption of Gu 

 radiation by Fe. The points obtained from experiments on 

 absorption bv Ag do not fall exactly on the curve and have 

 been omitted. There appears in this case to be a small 

 displacement to the left. This might be caused by the one 

 value AgAg being slightly too large. But quite apart from 

 small possible errors of experiment, slight displacements to 

 left or right are to be expected, as absorption in Al does not 

 provide a perfect standard of reference — that is a perfect 

 scale of abscissae. 



We thus see that for all these substances there is little or 

 no variation in the shape of their absorption curves in the 

 region of their spectral lines of series K. The connexion 

 between the curve for a particular absorbing substance and 

 the spectral line of that substance is shown in fig. 1, A being- 

 placed vertically above the spectral line shown in the lower 

 portion of the figure. 



In order to investigate the shape of the absorption curve 

 in the region of the spectral line of series L, experiments 

 were made on the absorption of homogeneous beams of 

 X-rays by Au and Pt. The spectral lines of series L for these 

 elements is within the range of absorbability most easily 

 experimented upon. The results are given in Table I. (p. 990). 

 If now we compare the shape of the curves by arranging 

 that the absorption of Au radiation (series L) in Au and of 

 Pt radiation (series L) in Pt is coincident on the figure with 

 the point A corresponding to Zn radiation (series K) in Zn, 

 &c, we at once see a marked difference. Curve L (fig. 1) 

 passes through points obtained by these experiments on Pt 

 and Au. It possesses similar characteristics to curve K, but 

 the ordinates are of very different magnitude. Thus the 

 shape of the absorption curves in the region of a spectral 

 line depends on the series to which the spectral line belongs 

 and not to any appreciable extent upon the particular 

 element in which the absorptions are made. 



By a combination of the two curves K and L we get one 

 absorption curve which is characteristic of every element 



